GRAVITY AND MAGNETIC MODELING OF THE HIKURANGI PLATEAU

Gravity modelling of the Hikurangi Plateau, east of North Island, New Zealand, indicates the crust thickens from about 10 km in the north to about 15 km adjacent to the Chatham Rise. It appears to thicken by a lesser amount to the west, towards the Hikurangi Trough. The Chatham Rise crustal thickness is 23-26 km, thinning to the south towards the Bounty Trough and east of the Chatham Islands. The gravity models indicate the eastern margin of the Hikurangi Plateau intersects the Chatham Rise at about 176-degrees-W. The area north of the Chatham Rise and east of 176-degrees-W could be either part of the Hikurangi Plateau crustal block, or oceanic crust thickened by sedimentary deposits. Postulated segmentation of the down-going slab beneath the North Island is not reflected in variations in crustal structure east of the trench. Magnetic modelling confirms the interpretation from seismic reflection data of widespread volcanism much of which may date from plateau formation.